Summary: The predominant proteins in the outer membranes of N. gonorrhoeae are trimeric porin proteins (PI). They are considered good vaccine candidates because porin protein is expressed by all strains, they are surface exposed, and, although antigenic variation exists between different strains, there is no phase variation during an infection as there is for both pilin and lipooligosaccharide (LOS). A model of these neisserial porin proteins predicts eight surface exposed loops. Regions of variability between serotypes in the genes coding for these proteins have been mapped and it is predicted that these variable region (VR) loops form the epitopes for both serotyping and bactericidal antibodies. A genotyping method to differentiate VRs of PIB strains of N. gonorrhoeae has been developed. Initially five collections of gonococcal isolates were typed using this method: (1) 24 endemic Korean strains from experimental vaccinees, (2) a panel of 17 temporally and geographically diverse strains, (3) a group of partner strains from a Baltimore STD clinic, (4) additional partner strains, (5) strains with published sequences for reference (Dr, M. Hobbs, North Carolina). The results suggested that in a group of temporally and geographically related strains there is a limited degree of variation in regions of the PI protein that are of suspected immunologic importance. Differences between strains of the same serovar and similarities between strains of different serovar were found illustrating that a variable region specific typing system is preferable in studies designed to address questions about the antigenicity and protective potential of the PI gonococcal protein. A similar typing system has been developed for gonococcal PIA strains. Both PIA and PIB probes have been adapted for use in checkerboard hybridization experiments which allows for typing of up to 35 strains with up to 40 probes per hybridization. We are currently examining the molecular epidemiology of gonococcal PI protein VRs in strains collected over the past 10 years in the STD clinics of Baltimore City using our PI VR typing method. We have identified the por VR type of a collection of partner isolates and disseminated gonococcal infection strains, and compared the por VR typing system to the serovar typing system. The results of earlier experiments in which lipid tailed cyclic peptides in liposomes designed to mimic individual loops of the porin protein were used as immunogens are described in a manuscript that is in preparation. We are using methods developed in these experiments to begin to examine serum and mucosal immune responses to the porin proteins following natural infection with Neisseria gonorrhoeae.